Relay control responsive to overvoltage and undervoltage

ABSTRACT

A line voltage guard circuit having a network including neon lamps, resistor-capacitor timing branches, diodes and transistors, the network being connected to a switching relay to control the availability of the supply line voltage to apparatus utilizing same and to disconnect the supply line from the apparatus when the line voltage is either below a bottom limit for a definite length of time or above a top limit. The circuit automatically reconnects the line to the apparatus a predetermined time after the supply voltage returns to a value between the top and bottom limits.

United States Patent Adams [4 1 Apr. 18, 1972 54] RELAY CONTROLRESPONSIVE TO 3,493,838 2/1970 Gyugi ..323/D1G. 2 OVERVOLTAGE ANDUNDERVOLTAGE 3, 33,323; 15/1323 Ead?j ..3230l/ 1/)/t2(;.)%

, au ers [72] Inventor: William M. Adams, 746 Oak Lane, Bryan,

77801 Primary Examiner-J. Miller [22] Filed: July 24, 1970 AssistantExaminerl-1a rvey Fendelman 1 pp No I 57 965 AttorneyBerman, Davidsonand Berman [57] ABSTRACT [52] US. Cl. ..317/16, 317/31, 317/33 C, A linevoltage d guar circuit havmg a network including neon 17/36 317/22317/51 317/141. 3 17/ lamps, resistor-capacitor timing branches, diodesand transistors, the network being connected to a switching relay 2 tocontrol the availability of the supply line voltage to ap- 8] 0 141/8paratus utilizing same and to disconnect the supply line from theapparatus when the line voltage is either below a bottom 56] R f d limitfor a definite length of time or above a top limit. The cire erences ecuit automatically reconnects the line to the apparatus a UNITED STATESPATENTS grtzsleterrglined time:l 'iijftetr thersupply voltage returns toa value e een e 0 an o om 1111] s. 3,320,493 5/1967 Culbertson ..3l7/31X p 2,854,615 9/1958 Light ..317/31 X 7 Claims,4Drawing Figures I Ll 2;r e

20 f a c3 1 )6 Q] CS 7 WCdNMouea l .179 lf /i N5: w /8C/:cu,-r 5cm 5 \qMai/Q25 g [4 2/ 3- 9.5 .x v /2' R N5 Nf/ Q2 Q /3 1% 3 M) a 52 6a 22 M AfvA I O4 23 RELAY CONTROL RESPONSIVE TO OVERVOLTAGE AND UNDERVOLTAGEThis invention relates to line voltage guard circuits, and moreparticularly to a device for the protection of electrical apparatus fromdamage due to low and high levels of line voltage.

age. However, there are many reasons whereby this source voltage canbecome too low or high for normal operation,

resulting in costly electrical failures. For example, in using step-uptransformer circuitry, high values of line voltage may result inoperating voltage levels that exceed maximum voltage ratings.

Due to increased line loading, some electrical apparatus may be damagedby low levels of line source voltage. The present invention, utilizingthe source voltage as its own power source, samples the level of sourcevoltage present, compares it to regulated reference levels, and protectsthe electrical apparatus from being damaged by excessively high orexcessively low source voltage conditions.

It is an object of the present invention to provide continuous samplingof low, normaland high source voltage levels, re-

gardless of the on" or off status of the protected electrical apparatus.

It is another object of the present invention to provide an improvedmeans for disconnecting the protected electrical apparatus from damagethat could result from a source voltage that continues below a presetlevel for a predetermined period of time.

It is a still further object of the present invention to provide a meansfor disconnecting the protected electrical apparatus from a sourcevoltage that reaches a level above a preset high limit.

It is another object of the present invention to provide a means toautomatically reconnect the protected electrical apparatus to the sourceof supply voltage, after a predetermined period of time, only when thesource voltage is between preset low andhigh voltage limits.

It is a still further object of the present invention to provide animproved line voltage guard circuit which can operate from eitheralternating current or direct current voltage sources.

With these and other objects in view, the present invention contemplatesthe use of transistor circuits and neon glow tube voltage reference andtiming circuits a well-known characteristic of a gas-filled glow tube,such as a neon lamp, is that ionization and de-ionization occur at twodifferent voltage levels. These different levels provide a uniquecharacteristic that permits well-defined reference levels, a certainamount of circuit hysteresis and, if desired, visual indications of thestate of the voltage source, providing novel and important features inthe invention. Power for operation of these circuits is taken from thesource line voltage. Low and high voltage sampling circuits are providedseparately to permit accurate limit levels to be established. Containedwithin these circuits are provisions for delayed operation that furtherprotects the electrical apparatus. When desired, a magnetic switch maybe included either as an integral part of the device of the presentinvention or maybe an existing component of the protected electricalapparatus.

' Other objects and advantages of the invention will become apparentfrom the following description and claims, and from the accompanyingdrawings, wherein:

FIG. 1 is a schematic diagram of a low and high source voltage samplingdevice that protects electrical apparatus in ac cordance with theprinciples of the present invention.

FIG. 2 is a graph showing typical variations of the RMS values of sourcevoltage with respect to time.

FIG. 3 is a graph showing the interrupted source voltage available tothe protected electrical apparatus, employing a device such asillustrated in FIG. 1, when supplied by a source having the voltagevariation characteristic shown in FIG. 2.

FIG. 4 is a schematic diagram of an auxiliary transistor circuit whichmay be employed as a means of obtaining higher levels of relay coilcurrent for relatively large magnetic switches, if such large switchesare employed to control a load apparatus to be protected by the guardcircuit of the present invention.

Referring to FIG. I, assume that an alternating current voltage sourceof to I30 volts RMS is applied to the tenninals l1 and 12, designated assource voltage. A diode D and a capacitor c, are connected in series torectify and filter this source alternating current voltage to provide aDC voltage at 13' for the transistor and neon glow lamp circuits. Thelevel of this DC voltage will vary with variations of the applied sourcevoltage level.

As shown in FIG. 1, the resistor R,, and the capacitor C form a RCcircuit which can develop a voltage at a junction point 14 forenergizing a neon lamp NE, Said RC circuit delays the ionization of theneon glow lamp NE, because of the time required for charging thecapacitor C Thus, as shown in FIG. 1, it will be seen that the aforesaidRC circuit comprising R,,, and capacitor C is connected in seriesbetween the point 13 and a line wire 15 and that the neon glow lamp NE,is connected between the junction 14' and the line wire 15 through aresistor R,,. The delay of ionization of the neon glow lamp NE, providesan on delay time to permit sampling by other circuitry of the appliedsource voltage.

Consider now the source voltage as shown at the time point 1 of FIG. 2.Ionization of lamp NE, after the delay time will result in forward biasbeing developed across the series resistor R,, and applied to the baseof a transistor 0., through a current limiting resistor R Transistor Q,conducts at a saturated level, energizing a relay K, with direct currentsupplied from the rectifier D, and the capacitor C defining a filtercircuit. Thus, it will be seen from FIG. I that the power supply linewire 16' is connected through the rectifier D, and the capacitor C tothe power supply wire 15', and the winding of the relay K, is connectedbetween the junction point 17' and the opposite line wire 15' throughthe transistor 0,.

The energization of relay K, operates switch contacts which may beeither of the normally open type or the normally closed type and whichmay contain multiple poles, as may be necessary. Assume, for example,that the relay K, is of the normally open type controlling a pair ofcontacts 18 and 19 which close responsive to the energization of therelay, the contacts 18 and 19 being connected in series between thevoltage source and the load. Closure of these contacts occurs at a timeillustrated as time point 2 in FIGS. 2 and 3. The time differencebetween points 1 and 2 is the on delay time.

Let it be assumed that subsequent to the time point 2 an increase insource voltage occurs toward a limiting upper level A at a time point 3in FIG. 2. As will be seen from FIG. 1, the voltage at point 13' is thesame as at a point 20, the resistors R,, R and R being connected betweensaid point 20 and the power supply line 15'. Resistor R is apotentiometer, whereby the series resistors R,, R and R define a voltagedivider circuit connected so as to allow the ionization of a neon lampNE, to be set at a level corresponding to the high threshold value A.Ionization of the lamp NE, results in the establishment of forward biasfor a transistor 03, said forward bias being developed acrossseries-connected resistors R,, and R,,,, the bias voltage being appliedto the base of transistor Q through a current-limiting resistor R,,.Forward bias of transistor 0,, results in capacitor C, dischargingrapidly and lowering the voltage applied to the series branch comprisinglamp NE, and resistor R,, to a value below that required to maintainionization of lamp N15,. This removes the forward bias on transistor Q,and deenergizes relay I(,. The switch action of relay K, opens thecontacts 18-19 and disconnects the high source voltage from theprotected electrical appliance, the disconnection taking place at thetime point 4 in FIG. 3. The time point 4 is quite close to the timepoint 3 in FIG. 2.

A portion of the circuit of FIG. 1 comprising resistor R capacitor Cneon lamp NE,, resistor R,,, resistor R and transistor 0, defines arelaxation oscillator that periodically lowers the voltage applied toneon lamp NE supplied from the voltage divider circuit R,, R and R Neonlamp NE, therefore deionizes during each conduction period of transistorQ Source voltages above that of level A at time point 3 and the slightlylower level B at a time point 5 of FIG. 2 will result in neon lamp NE,again becoming ionized during non-conduction periods of transistor 0,.If, however, the source voltage decreases to a level below that of B atpoint 5, neon lamp NE, will deionize with the next conduction period oftransistor Capacitor C, is again permitted to charge for the on delaytime, at the end of which relay K, is energized applying the sourcevoltage to the protected electrical apparatus, for example, at timepoint 6 of FIG. 3.

Let us assume that subsequent to this time the source voltage decreasestoward a value C at a time point 7 of FIG. 2. An adjustable voltagedivider branch is provided between the point 20 and power wire 15'comprising resistors R R and R-,, the resistor R, comprising apotentiometer with its adjustable contact connected to the base of atransistor Q, through a current-limiting resistor R This adjustablevoltage divider branch circuit permits the selection of a base toemitter voltage, of transistor 0,, such that the conduction of Q, issufficient to cause the voltage drop across resistor R and resultantvoltage across NE, to be below the ionization level of NE,. When thesource voltage drops below value C at a time-point 7 of FIG. 2, theconduction of transistor Q, is such that additional current flows in theIt -C circuit, permitting C to charge to a higher voltage level, andpermitting NE, to ionize. Ionization of NE, is therefore delayed, withrespect to the time of the lower source voltage below value C attime-point 7. If a low source voltage exists for a period of timegreater than the charge time of capacitor 0,, NE, will ionize.

Similar to the ionization of lamp NE the ionization of lamp NE, resultsin the deenergizing of the relay K, and the disconnection of the sourcevoltage, at the time point 8 of FIG. 3, from the protected electricalapparatus.

Ionization of NE, results in a voltage drop across series-connectedresistors R,,, and R,,. A portion of this voltage is applied as emitterbias to transistor Q,. This emitter bias serves to shift the operatingpoint of transistor On such that the conduction of transistor 0, isdecreased and the current in NE,, R,,, and R,, is increased. Thisfeed-back arrangement prevents resetting of the system due to anapparent improvement of source voltage due to removing the protectedappliance load from the source.

The different threshold levels A and B at time points 3 and 5, as wellas the levels C and D at time points 7 and 9 provide a slight amount ofcircuit hysteresis that prevents cycling of relay K, at source voltagelevels just outside the low and high threshold settings.

Increased source voltages above the level D at time point 9 of FIG. 2cause neon lamp NE, to become deionized, and following the on delay timepreviously described, the relay K, energizes, making the source voltageagain available to the protected electrical apparatus, for example, attime point 10 in FIG. 3.

In the event of a high voltage transient E such as that which occurs atthe time point 11 in FIG. 2, the relay K, will become deenergized in themanner previously described, quickly removing the source voltage fromthe protected electrical apparatus, then, at the time point 12 in FIG.3.

Short-duration low line voltage transients may occur, for example, atthetime points 13 and 15 in FIG. 2. A longer duration source voltage dropout, for example, that which occurs at the time point 15, will result incapacitor C charging sufficiently to permit ionization of neon lamp NE,and consequently the deenergization of relay I(,, removing the sourcevoltage, for example, at time point 16 in FIG. 3, from the protectedelectrical apparatus.

Short intervals of restoration of adequate source voltage, such as inthe short time period 17 in FIG. 2, will not permit the on delay timingto be completed, and therefore prevents repeated starting surges of theprotected electrical apparatus.

A diode D, connected across the winding of relay K, prevents excessivecollector voltage on transistor O, which might otherwise be present dueto the high surge condition developing when relay K, deenergizes.

Terminals 21 and 22 are provided across the coil of relay K, andterminals 23 and 24 are provided in the emitter return circuit oftransistor Q, for external connections. The terminals 23 and 24 arenormally connected by a jumper 25. Additional current amplificationcircuitry, such as that shown in FIG. 4, can be employed at theseterminals to provide additional coil current, as may be required bylarge magnetic switches. Thus, the jumper 25 may be removed and aresistor R, connected across terminals 23 and 24 and a transistor Q, maybe connected to the coil of relay K, in the manner shown in FIG. 4 withterminal 23 connected to the base of the transistor and terminal 24connected to the emitter of the transistor, the collector of thetransistor being connected to one terminal of the coil of relay K, atthe terminal 22.

In the foregoing description, an alternating source voltage wasconsidered as being applied to the input terminals 11 and 12 of thedevice illustrated in FIG. 1. A direct current source voltage may alsobe used to supply the necessary power for the transistor and neon glowtube circuits. Since the neon glow lamps require ionization voltages offrom 60 to volts, source voltages above these values will be required tooperate the device. The rectifier diodes D, and D provide reversevoltage protection when direct current source voltages are used.

From the foregoing description, it will be apparent that in operation,when the source voltage is great enough to fire the glow discharge tubeNE, the impedance R provides a sufficient voltage drop thereacross toprovide forward bias on the control electrode of the transistor Qwhereby to cause energization of control relay I(,. However, the circuitoperates to provide forward bias on the control electrode of thetransistor 0,, connected across the series circuit comprising glow lampNE, and impedance R Therefore when the voltage source is at either thehigh limit value or the low limit value, as previously described, theseries circuit comprising neon lamp NE. and impedance R is substantiallyshunted, removing the forward bias from transistor Q, and causing therelay K, to become deenergized.

Many useful applications of the device will be obvious to those skilledin the art. For example, a typical application would be in connectionwith units containing electric motors employed under service conditionswhere the source voltage lingers below a fixed minimum level. The delayand hysteresis features of the device of the present invention areespecially important, since they require correction of source voltagelevels before normal operation of the protected electrical apparatus isrestored.

Another useful application would be for the control of an auxiliarypower plant. In this application, contacts would be closed to completethe power plants starting circuit. A similar device could be used tosample the power plants output voltage and continue to provideprotection of associated electrical appliances.

The following is a listing of a number of important features andadvantages of the device of the present invention:

1. It provides continuous sampling of low, normal and high sourcevoltage levels, regardless of the on or off status of the protectedelectrical apparatus.

2. It operates to disconnect the protected electrical apparatus from alow source voltage that exists below a preset level for a predeterminedperiod of time.

3. It operates to disconnect the protected electrical apparatus from ahigh source voltage when the source voltage attains a preset level.

4. It operates to automatically reconnect the protected electricalapparatus only when the source voltage is within the preset low and highvoltage limits for a predetermined period of time.

5. The device is operable from either alternating or direct currentvoltage sources.

6. The device operates to compare the sampled source voltage to neonglow tube reference voltages, establishing an inexpensive and improvedthreshold sensing point.

7. The device is arranged to allow auxiliary semiconductor circuitry tobe readily utilized for current amplification requirements of largemagnetic switch coils.

8. The device requires no external power supply other than the sourcevoltage, and the device is adapted to operate satisfactorily over widevariations of this source voltage.

9. The device embodies one basic unit, which can be expanded however, toprovide protection for any electrical apparatus designed to operate fromstandard commercial or auxiliary voltage sources.

While a specific embodiment of an improved line voltage monitoring andcontrol system has been disclosed in the foregoing description, it willbe understood that various modifications within the spirit of theinvention may occur to those skilled in the art. Therefore it isintended that no limitations be placed on the invention except asdefined by the scope of the appended claims.

What is claimed is:

1. In a control system, a control relay having switch contacts forconnecting a load device to a source of voltage, and means for actuatingsaid relay comprising circuit means including a series transistorconnecting said relay to said source, said transistor having a controlelectrode, a bias voltage branch circuit connected across said source,said branch circuit including a glow discharge lamp and an impedance inseries, means connecting the junction between said lamp and impedance tosaid control electrode, said impedance being sufficient to provideforward bias on said control electrode when the source voltage is greatenough to tire said glow discharge lamp, whereby to energize saidcontrol relay, means to substantially shunt the series-connected glowlamp and impedance, whereby to deenergize said relay, responsive to apredetermined limit value of source voltage, wherein said shunting meanscomprises a second transistor connected across said series-connectedglow lamp and impedance, said second transistor having a controlelectrode, and means to provide forward bias voltage to said last-namedcontrol electrode responsive to said limit value of source voltage,wherein said means to apply said last-named forward bias voltagecomprises a voltage divider impedance branch connected across saidsource, and circuit means including a second glow discharge lampconnecting a selected point on said voltage divided impedance branch tosaid last-named control electrode, said selected point corresponding toa predetermined high limit of source voltage, and means to periodicallylower the voltage applied to said second glow discharge lampsufficiently to periodically deionize said second glow lamp.

2. The control system of claim 1, and wherein said means to periodicallylower the voltage applied to said second lamp comprises a relaxationoscillator connected across a portion of said voltage divider impedancebranch.

3. The control system of claim 2 and the further means to apply forwardbias voltage to said last-named control electrode responsive to apredetermined low limit of source voltage.

4. The control system of claim 3, and wherein said further meanscomprises a second voltage divider impedance branch connected acrosssaid source, circuit means including a third glow discharge lampconnecting said last-named control electrode to a selected point on saidsecond voltage divider impedance branch, and a third transistorconnected across said third glow discharge lamp, said third transistorhaving a control electrode connected to said last-named selected point,

said last-named selected oint proyidin a conduction level of the thirdtransistor such that the third ow discharge lamp will ionize only at'asource voltage below said predetermined low limit.

5. The control system of claim 4, and means to delay ionization of saidthird glow discharge lamp.

6. The control system of claim 5, and wherein said delay means comprisesa series-resistance capacitance branch connected across said secondvoltage divider impedance branch, with the third glow discharge lampconnected between the resistance-capacitance junction of saidresistance-capacitance branch and one terminal of second second voltagedivider impedance branch.

7. The control system of claim 1, and delay means comprising a capacitorconnected across said series-connected glow lamp and impedance toprovide a time delay in applying forward bias voltage to said controlelectrode.

1. In a control system, a control relay having switch contacts forconnecting a load device to a source of voltage, and means for actuatingsaid relay comprising circuit means including a series transistorconnecting said relay to said source, said transistor having a controlelectrode, a bias voltage branch circuit connected across said source,said branch circuit including a glow discharge lamp and an impedance inseries, means connecting the junction between said lamp and impedance tosaid control electrode, said impedance being sufficient to provideforward bias on said control electrode when the source voltage is greatenough to fire said glow discharge lamp, whereby to energize saidcontrol relay, means to substantially shunt the series-connected glowlamp and impedance, whereby to deenergize said relay, responsive to apredetermined limit value of source voltage, wherein said shunting meanscomprises a second transistor connected across said series-connectedglow lamp and impedance, said second transistor having a controlelectrode, and means to provide forward bias voltage to said last-namedcontrol electrode responsive to said limit value of source voltage,wherein said means to apply said last-named forward bias voltagecomprises a voltage divider impedance branch connected across saidsource, and circuit means including a second glow discharge lampconnecting a selected point on said voltage divided impedance branch tosaid last-named control electrode, said selected point corresponding toa predetermined high limit of source voltage, and means to periodicallylower the voltage applied to said second glow discharge lampsufficiently to periodically deionize said second glow lamp.
 2. Thecontrol system of claim 1, and wherein said means to periodically lowerthe voltage applied to said second lamp comprises a relaxationoscillator connected across a portion of said voltage divider impedancebranch.
 3. The control system of claim 2 and the further means to applyforward bias voltage to said last-named control electrode responsive toa predetermined low limit of source voltage.
 4. The control system ofclaim 3, and wherein said further means comprises a second voltagedivider impedance branch connected across said source, circuit meansincluding a third glow discharge lamp connecting said last-named controlelectrode to a selected point on said second voltage divider impedancebranch, and a third transistor connected across said third glowdischarge lamp, said third transistor having a control electrodeconnected to said last-named selected point, said last-named selectedpoint providing a conduction level of the third transistor such that thethird glow discharge lamp will ionize only at a source voltage belowsaid predetermined low limit.
 5. The control system of claim 4, andmeans to delay ionization of said third glow discharge lamp.
 6. Thecontrol system of claim 5, and wherein said delay means comprises aseries-resistance capacitance branch connected across said secondvoltage divider impedance branch, with the third glow discharge lampconnected between the resistance-capacitance junction of saidresistance-capacitance branch and one terminal of said second voltagedivider impedance branch.
 7. The control system of claim 1, and delaymeans comprising a capacitor connected across said series-connected glowlamp and impedance to provide a time delay in applying forward biasvoltage to said control eleCtrode.